Process for preparation of 1-h-imidazo (4,5-b)pyrazin-2-ones



United States Patent Ofiice 3,549,633 Patented Dec. 22, 1970 3,549,633 PROCESS FOR PREPARATION OF I-H-IMIDAZO Y [4,5-b]PYRA'ZlN-2-0NES Edward J. J. Grabowski, Iseliu, Edward W. Tristram, Cranford, and Roger J. Tull, Metuchen, N.J., assignors to Merck & Co., Inc., Rahway, N.J., a corporation of New Jersey No Drawing. Filed Nov. 20, 1968, Ser. No. 777,479 Int. Cl. C07d 51/76 US. Cl. 260-250 Claims ABSTRACT OF THE DISCLOSURE A process is described for the preparation of 1H- imidazo[4,5-b]pyrazin-2-ones substituted in the 5 and 6 positions, which comprises heating of a 3-aminopyrazinohydroxamic acid or O-acyl derivatives thereof which causes rearrangement and ring closure to the subject compounds. The products demonstrate activity as antihypertensive agents.

This invention relates to a novel process for the preparation of 5-amino(or substituted amino) o-chloro-lH- imidazo [4,5-b]pyrazin-2 ones from novel 3 amino-5- amino (or substituted amino) 6 chloropyrazinohydroxamic acids and derivatives thereof. The process is represented by the following equation:

" (c) mononuclear arylcarbonyl, especially phenylcar- (d) lower alkylsulfonyl wherein the lower alkyl group has from 1 to about 3 carbon atoms, e.g.,

. methanesulfonyl, ethanesulfonyl, or propanesulfonyl, V

(e) mononuclear arylsulfonyl, especially phenylsulfonyl, either unsubstituted or substituted with such 2 as lower alkyl, of from 1 to about 3 carbon atoms e.g., methyl, ethyl and propyl;

R represents v v (a) hydrogen, v 1 V (b) lower cycloalkyl of from 3- to about 7 carbon atoms, e.g., cyclopropyl, CyclopentyL'cyclOhexyl, cycloheptyl and the like,

(c) mononuclear aryl, especially phenyl,

((1) lower alkenyl such as allyl,

(e) lower alkyl of from 1 to about 6 carbon atoms either straight or branched chain such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tort-butyl, pentyl, isopentyl, neopentyl, hexyl and the like, either unsubstituted or substituted with such as (1) lower alkoxy of from 1 to about 3 car- 'bon atoms, e.g., methoxy, ethoxy, propoxy and the like, (2) pyridyl, (3) mononuclear aryl, especially phenyl, either unsubstituted or substituted with halo, (4) amino, of formula,

wherein R represents (a) hydrogen, "(b) lower alkyl of from 1 to about 5 carbon atoms, e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec.- butyl, pentyl, isopentyl, neopentyl and the like, (c) lower alkylca-rbonyl, of from 2 to about 3 carbon atoms, e.g., acetyl, propionyl, and the like;

R represents (a) hydrogen, (b) lower alkyl, of from 1 to about 5 carbon atoms, e.g., methyl, ethyl, propyl, isopropyl, 'butyl, isobutyl, sec.- butyl, pentyl, isopentyl, neopentyl, and the like;

R and R when lower alkyl can be linked together either directly or through 'a hetero atom such as nitrogen or oxygen to form a saturated heterocycle of 56 members with the nitrogen to which they are attached, e.g., piperidino, pyrrolidinyl, morpholino, piperazinyl, N-lower alkyl-piperazinyl, and the like;

-R represents hydrogen or lower alkyl of 1 to about 3 carbon atoms such as methyl, ethyl and propyl; and R and R when lower alkyl can he linked together either directly or through a hetero atom such as nitrogen or oxygen to form a saturated heterocycle of 5-6 members with the nitrogen atom to which they are attached,

e.g., piperidino, pyrrolidinyl, morpholino, piperazinyl,

N-lower 'alkyl-p'iperazinyl, and the like.

The novel process of this invention involves a rearrangement of Compound I and subsequent ring closure to Compound II, and can be conducted either neat or in solution. The process comprises either heating Compound I in basic to neutral aqueous solution or in a solvent such as pyridine, quinoline or collidine at from 25 to about 100 C. for from one-half to about 2 hours, or by fusion of the starting material.

The products of the process of this invention are orally active, relatively non-toxic, highly eifective antihypertensive agents with a moderate degree of diuretic and saluretic activities. They can be administered in the form of pills, tablets, capsules, elixirs, injectable preparations, and the like, in compositions which comprise one or more of the compounds of Formula II as the only active ingredient or in combination with other therapeutic ingredients. The compounds are advantageously administered at a dosage range of from about 5 mg. per day to about 750 mg. per day per 70 kg. of body weight. The dosage can be given in subdivided amounts on a two-four time a day regimen.

Compounds of Formula II are tautomeric in nature and exist as 1H-imidazo[4,5-b]pyrazin-Z-ones (the structureshown in Formula II) and as the corresponding 1H- imidazo[4,5-b]pyrazin-2-ols (the structures shown by Formulae 11a and H11) as follows:

(Ila) Although the enol forms represented by Formulae Hz: and 11b may comprise a significant or predominant form of a given compound, for the sake of brevity, only one form is referred to throughout this specification. It should be understood, however, that the present invention is inclusive of the production of compounds represented by all tautomeric structures.

The novel starting materials for the process of this invention are prepared according to the following reaction schemes:

Compound IV is prepared by treating III in alcohol solution with an appropriately substituted amine. Conversion to V results from standard ester saponification techniques. The preparation of Compound VI is accomplished by treating the carboxylic acid V with n-(tbutyl)- S-methylisoxazolium perchlorate. The hydroxamic acid I (R=H) is then prepared by treatment of VI with hydroxylamine which is then further converted to I(R H) by reaction with the appropriate acyl chloride, or sulfonyl chloride.

The details of the reaction conditions for the various steps are readily apparent from the following preparations and examples.

PREPARATION 1 3-amino-5-ethylamino-6-chloropyrazinohydroxamic acid Step A: Preparation of methyl 3-amino-5-ethylamino- 6-chloropyrazinoate.-A suspension of methyl 3-amino-5- 6-dichloropyrazinoate (178 g., 0.8 mole) in 2-propanol (1.1 liters) is stirred while ethylamine (4.4 moles) in 2- propanol (2 liters) is added, and the mixture is refluxed for an hour. The product that separates on cooling is collected by filtration and dried. The yield is 89%. After recrystallization from 2-propanol, the methyl 3-amino- 5-ethylamino-fi-chloropyrazinoate melts at 149-1 50 C.

Analysis.Calculated for C I-I ClN O (percent): C, 41.66; H, 4.81; N, 24.29. Found (percent): C, 42.11; H, 5.05; N, 24.24.

Step B: Preparation of 3-amino-5-ethylamino-6-chloropyrazinoic acid.A mixture of finely ground methyl 3- amino-5-ethylamino-6-chloropyrazinoate (0.5 mole), isopropyl alcohol (1875 ml.) and 5% aqueous sodium hydroxide solution (625 ml.) is heated under reflux with vigorous stirring for 1 hour. Water (7500 ml.) is added to the cooled reaction mixture and the resulting clear solution is made acid to congo red paper by the addition of concentrated hydrochloric acid. The light yellow solid which separates is collected and dried. Recrystallization provides 3-amino-5-ethylamino-6-chloropyrazinoic acid.

Step C: Preparation of N-(t-butyl)-3-methyl-3-(3- amino 5 ethylamino 6 chloropyrazinoyloxy)acrylamide.-A mixture of 3 amino 5-ethylamino-6-chloropy'razinoic acid (0.01 mole), triethylamine (0.01 mole) and dimethylformamide (20 ml.) is stirred for 10 minutes. N-(t-butyl)-5-methyl isoxazolium perchlorate (2.40 g., 0.01 mole) is added and the resulting solution is stirred for 2 hours. Water ml.) is added and the solid which separates is collected and dried. Recrystallization from acetonitrile provides pure N-(t-butyl)-3-methyl- 3 (3 amino 5 ethylamino 6-chloropyrazinoyloxy) acrylamide.

Step D: Preparation of 3 amino 5 ethylamino 6- chloropyrazinohydroxamic acid.N (tbutyl)-3-rnethyl-- 3 (3 amino 5 ethylamino-fi-chloropyrazinoyloxy) acrylamide (0.3 mole) is dissolved in a minimum amount of tetrahydrofuran. Hydroxylamine (35 ml. of 10' M aqueous solution) is added and the solution is stirred for one hour. The solvent is removed under reduced pressure and the residue is recrystallized from methanol-water to afford 3-amino-5-ethylamino-6-chloropyrazinohydroxamic acid, M.P. 185-186 C. i V p p Following the procedure described in Preparation 1, Steps A, B, C and'D but substituting-for the ethylamine utilized in Step A an equivalent amount of an amine of structure NH-R R?,--followed by the saponification of Step B, esterification of Step C and treatment with hydroxamic acid as in Step D, there are produced the 3 amino 5- NR R -6-chloropyrazinohydroxamic acids described in Table I according to the following equation.

CQOQHa TABLE I R H R t n: 'omoorncfi H H 31F; H H H H e5 N(CH2)2 H N CH 1i Preparation:

-CH2CH2NC I2CH2 1G -CH2CHgOCH2CH2 C3 11 monoi- H 11- 41 I v 18 (0H3)2N(0H2)3- CH3- 19 (CzH5)2N(CH2)r- U F C 0 CH 2o H CHg-N-(CHa) 2- 21 CH3, GHQ-- 22. C2H5- C2lIfi H H 24 H H H H H H 31 Cl-CH2- H 32 I? CH2 H 33 (CH3)2N(CH2)2- H 35 CzH5- (1113- 37 -(CH2)21TI(CH2)2 EXAMPLE 1 5-ethylamino-6-chloro-1H--irnidazo[4,5- b] pyrazin-Z-one 3 amino 5 ethylamino 6 chloropyrazinohydroxamic acid (3.0 g., from Preparation 1) is heated at its meltirlg point C.) in an oil bath for 15 minutes after fusion is complete. After cooling, the solid mass is recrystallized from a mixture of ethyl acetate and hexane to give 5-ethylamino-6-chloro-lH-imidazo [4,5-b]pyrazin- 2-one, M.P. 248-249 C.

EXAMPLE 2 S-dimethylaminoethylaminm6-ch1oro-lH-imidazo [4,5-b1pyrazin-2-one Benzene sulfonyl chloride (0.1 mole) is added dropwise to a stirred solution of B-amino-S-dimethylaminm ethyIalminQ-G chloropyrazinohydroxarnic acid (0.1 mole, from Preparation 34) in 1 N sodium hydroxide solution (200 ml.). The reaction mixture is stirred at 25 C. for one hour, then acidified at 0 C. to pH 4 with dilute hydrochloric acid. The product that precipitates is collected by filtration, dried and recrystallized to give 5- dimethylaminoethylamino ethylamino 6 chloro 1H- imidazo [4,5 -b] pyrazin-Z-one.

Employing the procedures substantially as described in Example 2 but substituting for the 3-amino-5-dimethylaminoethylamino-6-chloropyrazinohydroxa:mic acid and the benzenesulfonyl chloride utilized therein, equivalent quantities of 3-amino-5-NR R -6-chloropyrazinohydrox amic acid and the sulfonyl chloride as identified in Table II there are produced the 5-NR R -6-chloro-IH-imidazo [4,5-b1pyrazin-2-ones also described in Table II.

t TABLE II R1 N R1\ N R!\ N g /N -NHz RC1 /N NHg /N L 01 I 001111011 c1 c NIIOR 01 \N/ \\N/ \N/\N H Starting material from M.P. preparation R R R 0.)

Example:

a 2 CHsOCHZCIiT H c1H1s01- 229-231 4 a H OHz-Q-SOz- 280 CH:- 4 II CH,- sow- 271-272 5 CH;,CONH(OHz)z H cmcmsm- 235-238 6 i-PrNH(CH2)3 H CHaCHzSOr- 190-192 7 0H300NH 0Hz)3-' H CHJSOT- 226-227 8 (C'2H5)2N(CHz)2- H CHaS02- 276-278 EXAMPLE 10 tion and warmed at 50 C. for minutes. After acidifica- 5-dimethylaminopropylamino-6-chlorolH-imidazo [4,5 -b] pyrazin-Z-one A solution of benzenesulfonyl chloride (0.1 mole) and 3 amino 5 dimethylaminopropylamino 6 chloropyrazinohydroxamic acid (0.1 mole, from Preparation 9) in 100 ml. of pyridine is warmed at 50 C. for 1 hour.

After cooling the reaction mixture is quenched by pouring into an excess of ice-water mixture. After stirring until the ice has disappeared, the precipitate is collected by filtration and dried carefully.

The hydroxamic acid ester isolated above (0.1 mole) is dissolved in 100 ml. of 1 N ammonium hydroxide solution to pH 4 with concentrated hydrochloric acid the product 5-dimethylaminopropylamino-G-chloro-1H-imid- TABLE III N N i N ii N -NHz N NH: N R 01 R2 01 CONIIOII 01 c NHOR R2 01 H I I Starting material from M.P. preparation R R R 0.)

Example 11 10 (CH3) 2N (CH2)|- H CeHsSOw- 278-279 12 11 N(CHz)z- H omQ-sm- 149-150 13 12 CHaN\ N(CHz)a 11 cmQ-sm- 167-169 14 13 O N- (C Hz)a- H CHaCHzSOr- 154-156 15 l4 CH3(CH2)2- H CHaCH2SO2 215-216 CzHs 16 15 (CH2)2-N(CH2)2 CH3SO2-- 307 17 16 --(CH2)2O(CHz)z- CHgSOr- 212-273 (111 18 17 N-(CH2)z- H CHzCO- 254-255 l'l-ClHg 19 1 18 (CHa)2N (CH2)a- H CHaCO- 229-230 20 19 (02115) 2N (CH2)2- H CuIIgCO- 244 C OCH;

21 2O CH3N(CH2)2- H CoHsC O 227-228 21 CH;;- CH:- CoHaCH2CO 216-217 22 C2H C2Hs- CaHtCH2CO- 207-208 23 H CHaCHzCO- 300 24 CHa- H CHzCH2CO 280 azo[4,5-b]pyrazin-2-one is collected on a filter, dried the 3-amino-S-dimethylaminopropyl-'- 9 EXAMPLE 26 5-propylamino-6-chloro-lH-imidazo[4,5-b1pyrazin-2-one A solution of benzenesulfonyl chloride (0.1 mole) and 3-amino-5-n-propyla1nino 6 7 chloropyrazinohydroxamic The above formulation employing more or less active m gredients or awcornbinationgof active ingredients can be employed to prepare capsules ofthe other; nov el compounds of this invention hereinbefore' described. 5

acid (0.1 mole, from Preparation 25) in 100; ml. of 1 N 5 H fi i' p a sodium hydroxide solution is warmed at 50 C.for lhour. nnhalafl'on Sol mi f 5 m1 I; I After diluting largely with water and cooling to 5 C. a i 'f g flgg g gifi j ffim' preclpitate forms whlch is collected on a filter, washed y y A v wenwith W a d dried: a a The hydroxamic acid ester isolated above (0.1 mole) is 5 6; m t a dissolved in 100 ml. of 1 N ammonium hydroxide'solui, ,2{3gg;, f ;?1 am it tion and warmed at 50 C. for 30 minutes. Afteracidificag g irf 0.530 .79. 5 tion to pH 4 with dilute hydrochloric'acid the product f 25.115 S-propylamino 6 chloro-lH-imidazo[4,5-b]pyrazin 2- 15 l I: p one precipitates and is collected by filtration, dried and recrystallized from a mixture of ethyl acetate and hexpfoceduref A f? h l 3 ane. n has a M.P. 215-216 c. 6 1H fh f 2 "F Employing the procedure of Example 26 but substitut- {more and 795 Fremf l1 Fh Q flF P}h4 ing for the 3-amino-5-n-propylamino-6chloropyrazino-hym a 2 0 capaclty Plastlc qg q t p pe pdroxamic acid and the benzenesulfonyl chloride utilized prox'mathly loo'gm; 0f 6 m glasrsibe-adsfts 9 therein equivalent quantities of the 3-amino-5-NR B -6- for 48 hours to f the h f P :l1CIeS1Z"0f less chloropyrazinohydroxamic acids and the acid chlorides dethan 1- A Sufficlem qh y the milled concentrate scribed "in Table IV there are produced the 5-NR R -6 cooled to an PPI P E' te perature is transchloro-lH-imidazo[4,5-b]pyrazin-2-ones also described in ferred to each of the Dre-Cooled chhtalhers- The required T bl IV, v amount of Freon 12/114 (dichlorodifluoromethane/1,2- TABLEIV R1 q H R1 I R1 H CNHOR c1 01 \N CONHOHY 01 \N H I \N g W Starting material from M.P. preparation R1 R1 R 0 Q) it??? 26 CHz=CHCH2 H CtHaSO2- 224-225 2s 21 n-C4Ha' H c r-Q-SOr- 191-198 29 2s rot H1; i a Q H G 's-QB 02- 247-249 30 29 t-o4m. .:H om-om-soh 2 31 30 Y I H onaomsoh 256-257 32 at o1--ffi QH cHss'oP" as 32 N CH2% H ornsol a4 34 H onloo- 35 35 can I t, omoH,oo- .7 36 36 (CH2)5 curled-1f 37 37 konnm wnab 0011509 Formulation 1 I; Dry filled capsule containing mg. of active ingredient Mix the 5 cthylamino 6 chlo r o- 1H imidazo [4,5 b] pyrazin 2 one and lactose and reduce to a No.

mesh powder. Encapsulate, filling 325 mg. in each No 2 capsule.

dichloro-l,1 ,2;2) tetrafluoroethane) is addedand the container is sealed under pressure with'a metering valve fitted with a plastic actuator and mouthpiece- F0 RMULATIONB Procedure: The drug is dispersed in the Freon 11 (trichlorofiuoromethane), milled to the desired particle size in the manner described in Formulation 2 and subdivided into the individual containers. Sufficient Freon 12/114 (dichlorodifluoromethane/1,2 dichloro 1,1,2,2 tetrafluoroethane) is added to each container. The ascorbic acid dissolved in the anhydrous ethanol is likewise subdivided into individual containers. All operations are performed at an appropriately chosen temperature. Finally, the containers are sealed in the manner described in Formulation 2. Dosage forms containing from 0.2 to 1.0 mg. of active ingredient per spray can be prepared in a manner identical to that described above.

While the invention has been described with particular reference to certain variables in the process conditions and compound substituents, it is to be understood that the invention embraces related processes and substituents which are obviousextensions of those disclosed.

What is claimed is:

1. A process for the preparation of -NR R -6-chloro- 1H-imidazo[4,5-b]pyrazin-Z-ones of structural formula wherein R is a member selected from the group consisting of hy (b) lower cycloalkyl of 3-7 carbon atoms, P y ((1) lower alkenyl, (e) lower alkyl, (f) lower( alkoxy-alkyl (g) pyridyl-lower alkyl, (h) phenyl-lower alkyl, (i) halophenyl-lower alkyl, (j) amino-lower alkyl wherein the amino group is of formula wherein R is a member selected from the group consisting of (1) hydrogen, (2) lower alkyl, (3) lower alkylcarbonyl, and R is a member selected from the group consisting of (1) hydrogen, (2) lower alkyl, and R and R when lower alkyl can be joined together to form a saturated heterocycle selected from the group consisting of piperidino, pyrrolidinyl, morpholino and N-lower alkyl piperazinyl; and R is a member selected from the group consisting of hydrogen and lower alkyl,

R and R when lower alkyl can bejoined together to form a saturated heterocycle selected from the group consisting of piperidino, pyrrolidinyl, morpholino and N-lower alkyl piperazinyl which comprises heating a compound of structural formula 12v wherein R is a member selected from the group consisting of (a) hydrogen, (b) lower alkylcarbonyl, (c) phenyl-lower alkylcarbonyl, (d) phenylcarbonyl, (e) lower alkylsulfonyl, (f) phenylsulfonyl, and (g) lower alkyl-phenylsulfonyl.

2. The process as claimed in claim 1, wherein R is lower alkyl, R is hydrogen, and R is as defined in claim 1.

3. The process as claimed in claim 1 wherein R is ethyl, R is hydrogen, and R is as defined in claim 1.

4. The process as claimed in claim 1, wherein R is di(lower alkyl) amino-lower alkyl, R is hydrogen and R is as defined in claim 1.

5. The process as claimed in claim 1 wherein R is dimethylaminoethyl, R is hydrogen, and R is as defined in claim 1.

6. A process for the preparation of 5-ethylamino-6- chloro 1H imidazo[4,5 b]pyrazin 2 one which comprises heating 3 amino 5 ethylamino 6 chloropyrazinohydroxamic acid to its melting point.

7. A process for the preparation of S-dimethylaminoethylamino 6 chloro 1H imidazo[4,S-b]pyrazin-2- one which comprises heating benzenesulfonyl 3-amino-5- dimethylaminoethylamino-6-chloropyrazinohydroxamate.

8. A compound of structural formula wherein R is a member selected from the group consisting of (a) hydrogen, (b) lower alkylcarbonyl, (c) phenyl-lower alkylcarbonyl, (d) phenylcarbonyl, (e) lower alkylsulfonyl, (f) phenylsulfonyl, and (g) lower alkyl-phenylsulfonyl, R is a member selected from the group consisting of (a) hydrogen, (b) lower eycloalkyl of 3-7 carbon atoms, p y (d) lower alkenyl, (e) lower alkyl, (f) lower(alkoxy-alkyl), (g) pyridyl-lower alkyl, (h) phenyl-lower alkyl, (i) halophenyl-lower alkyl, (j) amino-lower alkyl wherein the amino group is of formula wherein R is a member selected from the group consisting of (1) hydrogen, (2) lower alkyl, (3) lower alkylcarbonyl, and R is a member selected from the group consisting of (1) hydrogen, (2) lower alkyl, and R and R when lower alkyl can be joined together to form a saturated heterocycle se- 13 14 lected from the group consisting of piperidino, 13. The compound of claim 8, wherein R is di-(lower pyrrolidinyl, morpholino and N-lower alkyl alkyl)amino-lower alkyl and R is hydrogen. piperazinyl; and 14. The compound of claim 8 wherein R is di-(methyl) R is a member selected from the group conaminoethyl and R is hydrogen.

sisting of hydrogen and lower alkyl, 15. The compound of claim 8 wherein R is di-(methyl) R and R when lower alkyl can be joined together to aminoethylandRand R are hydrogen.

form a saturated heterocycle selected from the group consisting of piperidino, pyrrolidinyl, morpholino and References Cited N-lower alkyl piperazinyl. UNITED STATES PATENTS 9. The compound of claim 8, wherein R is hydrogen. 3 361748 1/1968 C t 1 10. The compound of claim 8 wherein R is lower alkyl 10 3:410:850 11/1968 5223: 260 250 and R is hydrogen.

11. The compound of claim 8 wherein R is ethyl and NICHOLAS S. RIZZO, Primary Examiner R i hydrogen.

12. The compound of claim 8 wherein R is ethyl, and 15 R and R are hydrogen. 260-2472; 424-250 

